Dyestuff bleaching catalysts for the silver dyestuff bleaching process



United States Patent 3,443,949 DYESTUFF BLEACHING CATALYSTS FOR THE SILVER DYESTUFF BLEACHING PROCESS Alfred Oefiker, Fribourg, and Rudolf Mory, Dornach,

Switzerland, assiguors to Ciba Limited, Basel, Switzerland, a Swiss company No Drawing. Filed Oct. 15, 1965, Ser. No. 496,663 Claims priority, application Switzerland, Oct. 22, 1964, 13,719/64 Int. Cl. G03 1 72 US. Cl. 96-73 4 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to dyestufI" bleaching catalysts for the photographic silver dyestuff bleaching process. The catalysts, which correspond to the formula N R NH;

in which R represents an aryl, an alkyl, a cycloalkyl or a heterocyclic radical, is incorporated in a layer free from bleachable image dyestuif of a photographic material for the silver dyestufi bleaching process. This material contains on a support in addition at least two silver halide emulsion layers containing bleachable image dyestufls. At areas of high exposure pure whites are obtained.

The present invention relates to dyestufi bleaching catalysts for the silver dyestuif bleaching process.

As is known, the production of coloured photographic images by the silver dyestutf bleaching process is based on the principle that organic dyestuffs, especially azo dyestuffs, are destroyed by metallic silver in suitable baths. Generally, these baths contain a mineral acid, for example, hydrochloric acid, or a strong organic carboxylic acid, potassium bromide and a compound capable of forming silver complexes, for example, thiourea. Theoretically, four silver atoms reduce one azo group with formation of colourless amines. However, azo dyestuffs differ greatly from one another in respect of their behaviour in this reduction process, the difierences being mainly in the time required to bring about reduction to a colourless substance. Furthermore, the silver dyestuff bleaching process is generally not carried out to its conclusion with utilization of the total amount of metallic silver present, but is terminated after a certain period after only a proportion of the said silver has been consumed. Thus, during a prolonged bleaching period, bleaching continues at those areas where metallic silver is still present, which means that there may be a paucity of half-tones, particularly at areas of low colour density.

As is known, a catalyst is required in the bleaching of some azo dyestuffs in order to equal out to a large extent the bleaching times for the different dyestuffs, and, where necessary, to permit bleaching to a pure white. Compounds that have been proposed as bleaching catalysts and some of which have been used successfully are, for example, 2,3-dimethylquinoxaline, 2,3-diaminophenazine, 2-hydroxy-3-aminophenazine and anthraquinone sulphonic acid. The catalysts are added to the silver dyestufi bleaching bath in the usual manner or are incorporated in the photographic colour layer. It is also known to add the catalysts to a bath preceding the silver dyestuif bleaching bath (see German application No. 1,154,- 345, which is open to inspection). Thus, there are al- Patented May 13, 1969 ready a number of catalysts and methods of using them available. Nevertheless, the use of catalysts is frequently beset with difiiculties.

The observation has been made that very good results can be achieved when catalysts of a specific composition and which are as free from colour as possible are incorporated in particular layers. Accordingly, the present invention provides photographic material for the silver dyestuff bleaching process which contain, on a support, at least two silver halide emulsion layers containing bleachable image dyestufifs, and also a layer free from bleachable image dyestulr which contains a dyestufi' bleaching catalyst which is non-diliusing in a neutral to alkaline medium, but which is capable of diliusing in an acid medium.

These conditions in respect of solubility can be met by catalysts of different constitution, especially by those that are free from acidic groups imparting solubility in water and that contain at least one basic nitrogen atom. They correspond, for example, to the formula N R NHz in which R represents an aryl residue, an alkyl residue or a cycloalkyl residue or a heterocyclic residue. These aminoquinoxalines, too, must be free from acidic groups imparting solubility in water. However, the residues R may also contain other substituents, for example, alkyl groups, alkoxy groups or halogen atoms. Cyclic residues are preferably monocyclic. As examples there may be mentioned compounds of the formulae Also suitable as catalysts are dibenzoquinoxalines, -for- The catalysts are incorporated in a layer free from bleachable image dyestutf. Thus, for example, the multilayer material may contain an additional gelatine layer that contains only the catalyst, which layer may be disposed immediately on the support or between two colour layers. In the latter case, the layer containing the catalyst also serves as separating layer. Furthermore, the catalyst may also be incorporated in a filter layer containing colloidal silver or an organic yellow filter dyestufi or in overcoating layers. Such filter layers, as Well as the layers containing the image dyestuffs, advantageously contain gelatine as layer colloid. The content of catalyst, based on anhydrous gelatine, is preferably 0.5 to 5%. The multilayer material may otherwise be made up of the usual components. It can also be advantageous to combine the catalyst layers to be used in accordance with the invention with other catalysts, for example, to add suitable catalysts having the above-mentioned composition or some other composition to the layers containing image dyestufif.

Photographic images in colour can be produced in known manner with the photographic materials of the composition indicated. It may also be advantageous to make use of catalysts in the treatment baths, for example, in the silver dyestuff bleaching bath or in a bath preceding the bleaching bath, in addition to the dyestuff bleaching catalysts already present in the material itself.

The following examples illustrate the invention. Unless otherwise stated, the parts and percentages are by weight.

EXAMPLE 1 HaOOSOrHN on is coated in known manner on a photographic material support. A gelatine intermediate layer of the following composition is then coated on the above layer:

The usual additives, for example, wetting agent and hardening agent, as well as 60 parts by volume of a 1% solution of the dyestutf bleaching catalyst of the Formula la in methanol are added at 30 C. to 1,000 parts of a 2% gelatine solution. The whole is then filtered and adjusted to the desired viscosity by the addition of water. A layer 1.5 thick (in the dry state) is produced by coatingat a temperature of 30 C. and at a rate of 6 metres per minute.

A green-sensitized magenta layer containing the dyestulf of the formula SOaH SOaH

a yellow filter layer containing the dyestulf of the formula a layer containing the yellow image dyestuif of the formula and a protective layer are then coated on the said intermediate layer in the usual manner.

The material so prepared is then exposed to red, green and blue light behind a neutral wedge filter, developed in a bath containing 1-methylamino-4-hydroxybenzene sulphate and hydroquinone, treated in a stop bath containing acetic acid, washed with water for one minute and then treated in a dyestulf bleaching bath comprising 20 parts by volume of hydrochloric acid of 37% strength, 50 parts of potassium bromide, 20 parts of thiourea and water to bulk the bath to 1,000 parts by volume. The duration of treatment in the dyestuff bleaching bath is just long enough to bleach the dyestuff completely at the areas most highly exposed; the time can be determined by experiment. Residual silver bromide and residual silver are removed in known manner.

EXAMPLE 2 With two exceptions, the procedure is the same as that followed in Example 1.

(1) The 60 parts by volume of a 1% solution of the dyestutf bleaching catalyst of the Formula 1a in methanol O-CgH HO NH-OzS CH:

Hons

as used in the preparation of the gelatine intermediate layer are replaced by 60 parts by volume of a 1% solution of the dyestufi bleaching catalyst of the Formula 2 in acetone.

(2) The dyestuff bleaching bath contains in addition, ml. of a mixture comprising 400 ml. of benzyl alcohol, 400 ml. of diethylene glycol and 200 ml. of water per litre of bath.

Control material is prepared in exactly the same manner, but without the bleaching catalysts of the Formulae la and 2. When this material was processed in the same manner, only a minute proportion of the image dyestutf is bleached, even when the bleaching time is extended to 30 minutes.

The catalysts of the Formulae 1a and 2 used in Examples 1 and 2 also produce good results when incorporated in other auxiliary layers, namely, in an undercoating layer, a filter layer or an overcoating layer.

What is claimed is:

1. Photographic material for the silver dyestuff bleaching process, which contains on a support at least two silver halide emulsion layers containing bleachable image dyestuffs and a layer free from bleachable image dyestufi" which contains a dyestulf bleaching catalyst corresponding to the formula v N Rf NH: R \q/ in which R represents a member selected from the group consisting of an aryl radical, an alkyl radical, a cycloalkyl radical and a heterocyclic radical.

2. Photographic material as claimed in claim 1, wherein the dyestuff bleaching catalyst corresponds to the formula 3. Photographic material as claimed in claim 1, wherein the dyestuff bleaching catalyst corresponds to the formula 4. Photographic material as claimed in claim 1, wherein the dyestufi bleaching catalyst corresponds to the formula References Cited UNITED STATES PATENTS 2,410,025 10/ 1946 Gaspar 9699 3,278,303 10/1966 Meyer et a1. 9653 J. TRAVIS BROWN, Primary Examiner.

US. Cl. X.R. 9620, 53 

